Recently, IEEE (Institute of Electrical and Electronic Engineers) has been standardizing a radio communication scheme called WiMAX (Worldwide Interoperability for Microwave Access). In WiMAX, there are IEEE 802.16d and IEEE 802.16e. IEEE 802.16d is for non-movable subscriber stations and IEEE 802.16e is for movable subscriber stations. The movable subscriber stations include mobile stations (MS). Further, IEEE 802.16m is being standardized as a next-generation standard of IEEE 802.16e.